1. Field of the Invention
A washer for washing photographic sheet material.
2. Description of the Prior Art
The archival processing of photographic prints and film is a technique designed to enhance the useful life of the print and film, so that it may be stored, exhibited and/or shown and viewed in museums and the like, for many years without fading or otherwise deteriorating. Ideally and theoretically, photographic print and film should last in good condition for over two hundred years, if properly washed free of the processing chemicals used in the making of the finished product print and film. Most photographic prints and films in the prior art have not been processed by procedures or techniques which insure maximum possible permanence, principally because inexpensive technology, facilities and apparatus is not generally available at a reasonable cost to accomplish this. Also, the laborious hand process for rendering a print archival, was too time-consuming to be feasible for the entire production of a photographer. Thus, most photographers are familiar with the results of improper processing and storage of photographs. Old photo albums are usually excellent case studies of photographic fading, staining, and other forms of degradation.
One of the most tedious steps in the prior art of making a permanent print free of stain and/or fading over long periods of time was the washing process, in which residual sodium thiosulfate (fixer, hypo etc.) and other chemicals used in the development, fixing and toning of photographs are washed off of the print or film and removed using hypo-eliminator solution, followed by extended washing of the finished print or film with water. Thorough washing requires that all areas of the photographic material be subjected to a constant flow of water, coming into contact with all surface areas of the sheet for sufficient periods of time so that residual chemicals diffuse and are carried away from the photographic emulsion and its support base. Most prior art print washers cannot satisfactorily be used to wash more than a few prints at a time if archival results are to be achieved. Most print washers have no adequate provision for keeping prints separated during the washing process, and also suffer from low water exchange rates due to the large volume of water they hold. Previous print washers do not set up a circumferential, hydrodynamic flow at a steady rate, that consistently reaches all areas of the prints.
Thus, most photographers interested in making archival prints have had to settle for the time-consuming method of hand-rotating prints in trays of running water. In addition, heretofore most washers designed to wash paper photographic prints have had no provision for insuring the separation of one print from another, which is necessary if a constant flow of clean water is to reach all areas of the print. Most previous print washers attempt to move the prints about by some physical means, in an effort to separate the prints from each other from time to time. This movement often results in damaged corners of the prints or abraded emulsions, especially with large-size prints. Attempts to separate prints by physical means, such as high velocity water jets, rotating drums etc. have generally been ineffectual with large-size prints, and have generally resulted in uneven or incomplete washing of the prints. Furthermore, most previous print washers hold a relatively large amount of water at any given time, which requires a large volume of water flow and long periods of time for the chemicals diffused from the prints to be diluted to a safe level. In addition, most previous print washers allow prints to float on the surface of the water when the washer is not in operation. This leads to uneven washing of areas of the prints. This means that prints should be removed from such washers soon after washing is completed, which places limits on the automatic operation of such washers. In addition, all previous archival washers using any type of flexible separator were limited to prints 11.times.14 inches maximum, and could not accommodate larger size prints such as up to 16.times.20 inches.
In one prior art washer for sheets of photographic material, as described in U.S. Pat. No. 3,657,990, the washer tank has a fluid inlet near the bottom including an aerator for introducing a mixture of fine bubbles and water into a horizontal distribution manifold at the bottom of the tank. The top of the manifold is a horizontal septum perforated throughout its area with small perforations. The aerator has a vertical air inlet tube extending from the fluid inlet to above the overflow level of the tank. A number of parallel compartments are provided for holding individual sheets; these are so arranged that there can be no fluid contamination between compartments. Thus each print is washed in its own separate vertical compartment by a constant flow of air-turbulated water circulating on both sides of the print. This gives a wash to all parts of every print, while using only a small amount of water. The prints do not move physically while washing, instead the water circulates around them. This prevents damage to prints and print corners regardless of the length of wash time.
Another prior art procedure entails placing a stack of photographic print or film in a tray so that the stack is immersed in hypo-eliminator solution. The stack is shuffled like a deck of cards to accomplish manual mixing. Usualy 3 to 5 minutes were required for 12 photos typically 11 inches by 14 inches. Then the stack is placed in a tray of water, for rinsing the hypo-eliminator plus residual hypo from the print or film. Shuffling at this point in order to accomplish good washing usually required about one hour's time, which is impractical. In addition, leaving the stack in the tray for an hour was detrimental because the prints sometimes became stuck together, which was very bad for archival prints. Other disadvantages of this general procedure using a tray was that handling sometimes caused cracking of the prints, i.e. the emulsion would crack or the paper would crack. Usually the procedure required rough handling for an extended period of time, much too long for all practical purposes. In many cases, non-uniform rinsing took place because of the stack arrangement. The procedure was manual, expensive and tedious.
Non-archival print washers have also been used, but the problem was still sticking of the prints. Archival print washers do separate the prints, but there is non-uniform flow because of one inlet for the water and one outlet. The water speed varies as a function of the height of the print, leading to uneven washing. Also, in many previous archival washers, the water inlet is on the bottom and the outlet on the top, so that pockets of residual contamination (heavier than water) stay in the tank.
In addition, large amounts of water were required. One typical prior art archival print washer needed 5 to 8 gallons of water per minute, as well as a high pressure faucet. This washer still required two separate handling operations, i.e. one in a tray of hypo-eliminator solution, and the second in a tray of water. This washer also had the aforementioned print handling disadvantage. The vertical tank of the washer always had to be filled with water, otherwise, experience has shown that the joints swelled and eventually cracked if water was not left in; 5 gallons of water weighs about 42 pounds and storage is a problem. This procedure is also too time-consuming, typically 70 minutes being required for 12 prints 11".times.14" black and white, for both the hypo-elimination step and the print washing. Also this washer was not effective because there was still a slight amount of hypo on the prints, as proved by the conventional silver nitrate test, which showed slight traces of hypo stain. A feasible and practical archival print washer, in order to produce a print that will last two hundred years without fading, or a print of museum quality, must eliminate all hypo in order to achieve this result. Ordinary prints have residual hypo on their surfaces, and will fade in 15 to 20 years.